I would like to learn how to determine the correct amount of sugar that is needed to make jelly. I have found recipes for the more common jellies but when it comes to the exotic fruits or such there are no recipes. I am certain that it must have something to do with the S.G. of the fruit or do I use a Refractometer? Is there a total sugar target that I need achive? Also I have noticed that some recipes call for lemon juice. Am I suppose to have a specific PH value or range for the product?

Lemon juice contains high amounts of pectin, which is what helps jams and jellies set. Most fruit have pectin, but in varying amounts...some have more than others. The addition of a couple of tablespoons of lemon juice won't change the flavour of your jelly, but will increase pectin levels, enabling setting of your jelly.

To be on the safe side, I add lemon juice to all the jams and jellies I make. It never hurts to have more pectin.